1. Field of the Invention
The present invention illustrates a negative voltage protection system, and more particularly, the negative voltage protection system for reducing an intensity of negative voltage by using a comparison circuit.
2. Description of the Prior Art
With the advancement of techniques, various electrical devices with high operational performance are widely adopted. Nowadays, most electrical devices are required to perform high processing speed and low response time in conjunction with a high-level processor integrated to a micro volume circuit. Thus, the electrical devices can be operated by users at any time and in any place. For example, the specification of iPhone 5s states that an A7-typed processor is used. The specification of iPhone 6 Plus states that an A8-typed processor is used. Another example is that the central processing unit (CPU) of the personal computer is upgraded from Intel® Core™ i5 to Intel® Core™ i7. Specifically, power consumption and heat generation of the electrical device are increased since the clock frequency of the processor is increased. Thus, the performance of heat dissipation components such as heat dissipation fans, a water cooling system, thermally conductive adhesive, and a heat sink attracts more attention. Among these heat dissipation devices, a water cooling system has the best heat dissipation performance yet has a large circuit volume, high cost, and high noise. Thermally conductive adhesives and heat sinks have smaller volume with inferior heat dissipation performance since they only use a medium for conducting heat. As a result, heat dissipation fans become the most popular devices for dissipating heat in general electric devices.
Specifically, in a half-bridge circuit based fan motor circuit, when the fan motor performs a phase alternation process, an effect of negative transient voltage is occurred due to Lenz's law. Unfortunately, when the negative transient voltage exceeds a tolerant voltage, a driving stage of the fan motor circuit suffers a latch-up effect. As known, the latch-up effect can interfere with all operations of fan motor circuit, such as interferences of a driving circuit and a clock circuit. Further, when the fan motor circuit is operated under a short state, an overloading state, or an automatic shut-down state, an effect of the negative transient voltage becomes severe.
To avoid the effect of the negative transient voltage, a limiter is introduced to a level shift driving circuit of the fan motor circuit. By using the limiter, the negative transient voltage and an intensity of an electrostatic discharge can be mitigated. However, practicability of aforementioned method is limited in practice. For example, when a distance between a controller and the fan motor circuit with a large capacitor is very long, the negative transient voltage generated from the fan motor circuit may exceed an amplitude of 100 volts (for example, the negative transient voltage is −120 volts). Thus, the limiter may lose a capability of protecting the fan motor circuit from the effect of the negative transient voltage.